Ruthenium- or osmium-based catalysts play an important role in homogeneous hydrogenation reactions of various substrates for many years as summarized in the Handbook of Homogeneous Hydrogenation, 2007, Volume 1, Pages 45-70 (Edited by De Vries, Johannes G.; Elsevier, Cornelis J).
In recent years, novel types of five-coordinated ruthenium- or osmium-based catalysts have been developed.
In U.S. Pat. No. 5,057,581, a ruthenium-based complex of the formula (A) is disclosed (column 3, line 52). These complexes are used as selective hydrogenation catalysts for carbon-carbon double bonds.

In WO 2013/159366 A1, catalysts with a general formula (B) as shown below are disclosed. The ligand L1 represents a NHC-ligand such as N,N′-bis[2,4,6-(trimethyl)phenyl]imidazolidin-2-ylidene (SIMes) and L2 represents either the same ligand as L1, another NHC-ligand or a phosphine ligand such as PCy3 (formula (B.a)). These catalysts are used for preparing hydrogenated nitrile rubbers.
However, this catalyst has disadvantages, as it is limited in stability in humidified air.

In H. M. Lee, D. C. Smith, Jr, Z. He, E. D. Stevens, C. S. Yi, S. P. Nolan. Organometallics, 2001, 20 (4), 794-797 and N. J. Beach, J. M. Blacquiere, S. D. Drouin and D. E. Fogg. Organometallics, 2009, 28 (2), 441-447, mixed NHC-phosphine variants of the type RuHCl(CO)(PR3)(NHC) are disclosed, e.g. RuHCl(CO)(PCy3)(IMes) (formula (B.b)). It was found that the use of labile phosphines in combination with strongly donating NHCs had a positive effect on rates of catalysis.

In Mücke, P., Linseis, M., Zális, S., Winter, R. F. Inorganica Chmca Acta 374 (2011) 36-50, a ruthenium-based complex of the formula (C) is disclosed. The meaning for the R moiety is not limited unless it is not too bulky (page 41). No NHC ligands are disclosed as alternative substituents. The document is silent about the use of this complex for hydrogenation reactions. The use of the complex as a catalyst in the presence of a nitrile rubber polymer is not disclosed.

In Wilton-Ely, J. D. E. T, Pogorzeloc, P. J., Honarkhah, S. J., Reid, D. H., Tocher, D. A. Organometallics, 2005, 24, 2862-2874, a ruthenium-based complex of the formula (D) is disclosed (page 2869, Scheme 4). The meaning of the R moiety can be H or C═CHPh and the meaning of the R′ moiety can be H, Ph or CMe3. However, no complex comprising an NHC-ligand instead of the second phosphine ligand is disclosed. The document is silent about the use of the complex as a catalyst in hydrogenation reactions.

In Maurer, J., Linseis, M., Sarkar, B., Schwederski, B., Niemayer, M., Kaim, W., Zalis, S., Anson, C., Zable, M., Winter, R. F. J. Am. Chem. Soc. 2008, 130, 259-268, a ruthenium-based complex of the formula (E) comprising arylphosphine ligands is disclosed (page 260, structure 2a). However, no complex comprising an NHC-ligand instead of the second phosphine ligand is disclosed. The document does not mention the use of the complex as a catalyst in hydrogenation reactions.

In Farmer, J. D., Man, W. Y., Fox, M. A., Yufit, D. S., Howard, J. A. K., Hill, A. F., Low, P. J. Journal of Organometallic Chemistry 721-722 (2012) 173-185, a ruthenium-based complex of the formula (F) comprising arylphosphine ligands is disclosed (page 175, Scheme 2). The meaning of the R moiety is limited to N(C5H4Me-4)2, OMe, Me, CO2Me and NO2. However, no structure is disclosed with a PCy3 or a NHC-ligand. The use of the complexes as catalysts for hydrogenation reactions of unsaturated olefins is not disclosed.

In Buil, M. L., Esteruelas, M. A., Goni, E., Olivan, M., Onate, E. Organometallics, 2006, 25, 3076-3083, a ruthenium-based complex of the formula (G) comprising alkylphosphine ligands is disclosed (page 3078, Complex 7). However, no structure is disclosed comprising a NHC-ligand and a (cyclohexyl)phosphine. Furthermore, the use of the complexes as catalysts for the hydrogenation reaction of olefins is not disclosed.

The formula (G) is disclosed also in Werner, H., Estrueias, M. A., Otto, H. Organometallics 1986, 5, 2295-2299.
In Marchenko, A. V., Gerard, H., Elsenstein, O., Caulton, K. G. New J. Chem., 2001, 25, 1244-1255, a ruthenium-based complex of the formula (H) comprising alkylphosphine ligands is disclosed (page 1244, complex 2). No structure is disclosed comprising a NHC-ligand instead of one phosphine ligand. The document is silent about the use of this complex as a catalyst for hydrogenation reactions of unsaturated olefins. However, the document mentions that five-coordinate, 16-electron square-pyramidal complexes MHCl(CO)L2 (L=Pr3) provide a rich variety of reactions with unsaturated hydrocarbons.

In Jung, S., Brandt, C. D., Wolf, J., Werner, H. Dalton Trans. 2004, 375-383, a ruthenium-based complex of the formula (J) is disclosed (page 376, structure 7). However, no NHC ligand is disclosed. The complexes described in this document are inactive as catalysts in olefin metathesis. The document is silent about the use of these complexes as hydrogenation catalysts.

In Pan, Q., Rempel, G. L. Macromol. Rapid Commun. 2004, 25, 843-847, and in U.S. Pat. No. 5,057,581, a ruthenium-based complex of the above mentioned formula (J) is disclosed. The complex is used as a catalyst for the hydrogenation of Styrene-Butadiene Rubber. The hydrogenation is performed at temperatures of 135° C. and above. However, structures of the complex comprising a NHC-ligand instead of the second phosphine ligand are not disclosed. Furthermore, the use as a catalyst for nitrile rubber is not disclosed.
In Martin, P., McMagnus, N. T., Rempel, G. L. Journal of Molecular Catalysis A: Chemical 126 (1997) 115-131, ruthenium-based complexes of the above mentioned formulae (J) and (G) (page 116) are disclosed. These complexes have the hydrogenation activity at the same level as the RuHCl(PCy3)2 catalyst for the hydrogenation of C═C in nitrile-butadiene rubber. However, structures of the complex comprising a NHC-ligand instead of the second phosphine ligand are not disclosed.
In Chatwin, S. L., Mahon, M. F., Prior, T. J., Whittlesey, M. K. Inorganica Chimica Acta 363 (2010) 625-632, a ruthenium-based complex of the formula (K) (page 626, structure 8; as well as the description in section 2.4 on page 629) comprising NHC-ligands (IMes) as shown below is disclosed. The R moiety has the meaning of 2,4,6-trimethylphenyl. However, no use as a hydrogenation catalyst is disclosed as well as no complex structure comprising a(n) (alkyl)phosphine ligand.

In Roper, W. R., Wright, L. J. Journal of organometallic chemistry 142(1) (1977) C1-C6, a ruthenium-based complex of the formula (L) comprising arylphosphine ligands is disclosed (page C2). No structure is disclosed comprising a NHC-ligand. The use of the complexes as catalysts for the hydrogenation of unsaturated olefins is not disclosed.

In Rickard, C. E. F., Roper, W. R., Taylor, G. E., Waters, J., Wright, L. J. Journal of Organometallic Chemistry, 389 (1990) 375-388, a ruthenium-based complex of the formula (M) comprising arylphosphine ligands is disclosed (page 377). No structure is disclosed comprising a NHC-ligand. The use of the complexes as catalysts for the hydrogenation of unsaturated olefins is not disclosed.

In Dinger, M. B., Mol, J. C. Organometallics 2003, 22, 1089-1095, a ruthenium-based complex of the formula (N) is disclosed (page 1090, structure 4). The complex was found to be an active and selective alkene double-bond isomerization catalyst. No structure is disclosed comprising an NHC-ligand. Furthermore, the document is silent about the use of the complex as a catalyst for the hydrogenation of unsaturated olefins, especially for the selective hydrogenation of nitrile rubbers.

In Banti, D., Mol, J. C Journal of Organometallic Chemistry 689 (2004) 3113-3116, a ruthenium-based complex of the formula (O) comprising a NHC-ligand and a phosphine ligand is disclosed (page 3114, scheme 2, complex 5). In the NHC-ligand (SIPr), Dipp stands in all cases for 2,6-diisopropylphenyl. However, the document does not mention the activity of the complex as a catalyst for the hydrogenation of unsaturated olefins, especially nitrile rubbers.

In Dinger, M. B., Mol, J. C. Eur. J. Inorg. Chem. 2003, 2827-2833, a ruthenium-based complex of the formula (P) is disclosed (page 2827, complex 7). The hydrogenation of a small terminal-olefin (1-octene) was tested at 100° C., 1 to 4 bar H2 and a reaction time of 2 to 18 hours. The fully air-stable solid complex is described as an efficient hydrogenation catalyst at higher temperatures. Beside the hydrogenation product, the complex produces isomers. The hydrogenation activity of the complex towards the non-terminal olefin 2-octene is even lower. No complex structure is disclosed with a vinyl ligand which does not comprise a phenyl ring. The document is silent about the activity of the complex as a catalyst for the hydrogenation of nitrile rubbers.

With regard to the hydrogenation of nitrile rubbers, the current industrial processes often use expensive Rh-based catalyst systems like Wilkinson's catalyst (RhCl(PPh3)3) together with PPh3 as co-catalyst. After hydrogenation, extra time and costs must be spent to remove and recycle the expensive Rh-based catalyst.
It was therefore the object of the present invention to provide novel ruthenium- or osmium-based complexes which are excellent hydrogenation catalysts on the one hand and which show a high stability in air or water on the other hand. In particular, such complexes should provide a high hydrogenation activity for large-scale industrial use at ambient air reaction conditions.
An alternative object of the present invention was to provide a complex catalyst with such a high activity that no co-catalyst needs to be used anymore or recovery and recycling of the catalyst would no longer be necessary, resulting in catalyst costs reduction and subsequently in substantial process costs reduction. Compared to commercially available hydrogenated polymers as obtained nowadays with known catalysts, it is important that the hydrogenated polymers to be obtained by using any new complex catalyst must not show significant changes in the polymer properties and in its vulcanization behavior.
A further alternative object of the present invention was to overcome some of the problems of the state of the art catalysts, being: no gel formation, higher activity, higher stability in air or organic solution, higher stability over longer time, higher stability at elevated temperature, high hydrogenation activity at lower temperature and balancing between stability and activity.
This object has now been surprisingly solved by providing novel ruthenium- or osmium-based complexes comprising a phosphine ligand, a N-heterocyclic carbene (“NHC”) ligand and a vinyl ligand.